EFFECTS OF LEAF WETNESS DURATION AND TEMPERATURE ON DEVELOPMENT OF BLACK SIGATOKA DISEASE ON BANANA INFECTED BY MYCOSPHAERELLA-FIJIENSIS VAR DIFFORMIS

Severity of Black Sigatoka disease on banana leaves infected by either conidia or ascospores from two isolates of Mycosphaerella fijiensis var. difformis was influenced by temperature and leaf wetness duration. A film of water on the leaf surface was required for ascospore infection. Conidial infection was observed at a leaf wetness of 0-18 h. Initial foliar symptoms of Black Sigatoka disease required an incubation period of 14 days on leaves subjected to 18 h of leaf wetness after inoculation. Symptom expression was delayed 7-14 days at lower levels of leaf wetness. Disease severity increased with increasing leaf wetness duration. The optimal temperature range for disease development was 25-28 C. Older leaves were more conducive to disease development. The arcsin of disease severity as a linear combination of temperature, leaf wetness, and leaf age best described the infection response (R2 = 0.84-0.91). Differences in area under the disease progress curve were found between the isolates.